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1. Field of the Invention
The present invention relates to computer network technology. More particularly, the present invention relates to searching and forwarding of frames and computer addresses in a computer network.
2. Description of Related Art
A computer network generally comprises a set of conjoined computer devices that are communicatively linked so as to share resources such as storage devices, peripherals, applications, output devices, etc. The computing devices in a local area network (LAN) are typically connected to each other directly by cable connections. For organizational reasons, several devices in a network may be connected at a central connection point referred to herein as a hub. A hub typically has a plurality of ports that are each communicatively linked to one or more devices, such as a node, a switch, or a repeater. As used herein, the term xe2x80x9cnodexe2x80x9d refers to any device that can communicate with other computers in a network. The hub receives an incoming signal from a source node through one port and sends the incoming signal out to a destination node through one or more other ports.
A repeater is a very simple form of a hub. Repeaters extend the size of a network by joining multiple segments into a larger segment. Repeaters increase a network signal""s strength so the signal can be transmitted and received over a greater distance without a loss in quality. For example, the signal may have become degraded due to the distance traveled from the source to the repeater over the cable. The repeater regenerates the weak signal internally and forwards the signal out through all ports. This means that a repeater does not process data at all, but rather merely receives incoming signals and reconditions them for immediate transmission on all ports (except the originating port). That is, the repeater does not perform any analysis as to the destination address of the signal, but rather blindly sends the signal out through all is ports.
A repeater can significantly increase the traffic level of a network because the repeater outputs all incoming signals through every port. This may not present a problem in networks where communication traffic is relatively low. However, in networks where traffic volume is relatively high, small increases in communication traffic may significantly degrade the performance of the network.
Switches and bridges are more complex types of hubs that overcome the aforementioned drawbacks associated with repeaters. Unlike repeaters, switches and bridges include frame forwarding logic and perform basic signal filtering functions before transmitting an incoming signal. Whereas repeaters forward all signals through every port, switches and bridges only forward signals that are necessary and only forward the signals to the appropriate port based upon the destination address of the signal.
In relation to the Ethernet network standard, signals are transmitted through the network as frames of data that travel from the source node to the destination node. A frame is generally comprised of several fields of information, including two fields that denote the destination Media Access Control (MAC) address and the source MAC address for the frame. The source MAC address specifies the source node of the frame and the destination MAC address specifies the destination node of the frame. Each node in the network is identified by a unique MAC address, which comprises a 48 bit (6 byte) string. Six bytes of device ID allows for approximately 32 trillion (248) possible unique MAC addresses.
When a switch or a bridge receives an incoming frame, the switch or bridge examines the frame""s destination address. The switch maintains in internal memory a database of past frames. Through use of the database, referred to herein as an address table, the switch can keep track of which MAC addresses correspond to which ports on the switch. Upon receipt of a frame, the switch references the database and determines the port that is associated with the particular MAC address. The switch then forwards the frame to the correct port. Essentially, the switch checks its internal memory of past frames and determines whether to forward the frame to another port or to filter out the frame.
The speed at which a switch can forward a frame to the correct port is dependent on several factors, including the amount of time that it takes for the frame to search its address table, find the frame""s destination address and output the frame through the correct port(s). Ideally, an address table would contain enough data space to store each and every possible 6 byte MAC address. In such a case, the address table could contain an array of entries comprised of a complete listing of every single possible address and the port corresponding to each address. Upon receipt of a MAC address, the switch could then quickly search through the table and identify the appropriate port to which the MAC address should be forwarded.
However, as mentioned, there are approximately 32 trillion (248) possible MAC addresses that would have to be stored in such a table. In the real world, it would not be practical from a cost standpoint to maintain sufficient memory to store a table that contains each and every possible six byte MAC address. One way of reducing the amount of memory required for an address table would be to store a compressed or hashed version of the address in the table. However, this could result in collisions during searching as one or more different addresses could map to the same hash value.
Consequently, there is a need for a fast and efficient method of maintaining computer address forwarding tables.
Disclosed is an apparatus and method for storing and searching computer node addresses in a computer network system. The system is described in the exemplary context of storing and searching MAC addresses in an Ethernet system. The system comprises a frame forwarding device such as a switch. The switch includes two MAC address tables including a primary MAC address table and secondary MAC address table both for storing and searching MAC addresses.
The primary MAC address table is preferably stored in a memory that is external to the switch and the secondary MAC address table is preferably stored in a memory that is internal to the switch. The primary table is preferably sensitive in data entry size according to the bus width of the external memory and may have a slower access speed and larger size than the secondary table. In order to increase the searching speed of the secondary address table, a search module is configured to perform on a bandwidth that is optimized to the memory in which the secondary address table is stored.
In one aspect of the invention, the primary address table stores records that contain MAC addresses. The records are contained in storage locations that are referenced using a compressed or hashed value of the MAC address as a search index. In order to account for searching collisions that may result from different MAC addresses hashing to the same value, each record in the primary address table may be linked to a hash family of chain of records in the secondary table. Each hash family chain of records in the secondary address table contains MAC addresses that belong to the same hash family, or MAC addresses that compress to the same value.
Still further objects and advantages attaching to the system and to its use and operation will be apparent to those skilled in the art from the following particular description.